2. Field of the Invention
This invention relates to a method for manufacturing a decorative molding, more particularly a plastic-based decorative molding.
2. Description of the Prior Art
Plastic decorative moldings are conventinally used for decorating the edges of desks or tables or the like, or for decorating, protecting and/or covering projections provided on outer and inner surfaces of automobiles.
Conventional moldings having different lengths and the same cross sectional shape is usually used for multiple purposes multipurpose. Accordingly, moldings having different lengths are usually manufactured by a known plastic extrusion molding process in which elongated products having a uniform cross section can be continuously molded. The molded products obtained by the extrusion molding process are then cut at predetermined lengths, in accordance with the various uses of the decorative moldings. The cut ends of the decorative moldings must be, however, finished with special instruments, or must be subject to special surface treatments.
In order to eliminate the need for such a special finishing operation or surface treatments, it has been proposed to make a decorative molding from a plastic film on which metal, such as aluminum or aluminum foil, is vaporized. High consistency liquid plastic is fed onto the plastic film, so that the liquid plastic forms itself into a convex surface layer due to the interfacial force. The convex plastic is then cured, so that a plastic decorative molding having a convex profile can be obtained. In this way, the above mentioned finishing operation or special surface treatments can be dispensed with, since the ends of the products, i.e. the decorative moldings have round edges, due to the interfacial tention of the liquid plastic.
However, this alternative method raises another problem. When the liquid plastic is cured, the molding is entirely warped toward the side of the liquid plastic film, due to the mold shrinkage of the liquid plastic. In particular, an elongated product, such as a decorative molding causes a large shrinkage in the longitudinal direction, in proportion to the length, resulting in a large warpage at the opposite ends thereof. It goes without saying that a warpage occurs also in the direction of the width of the molding, but the warpage is negligibly small when the width is small, for example in the order of a couple of centimeters.
On the other hand, a surface of an object, such as a table or an automobile to which the decorative molding is to be attached is usually flat, or slightly convex. This flat or convex surface makes it impossible or difficult to firmly secure there to a decorative molding which warps toward the outer side of the plastic film, by means of an adhesive or the like. Even if the decorative molding could be adhered to the surface of the object in use, the decorative molding tends to peel off from the surface, at the opposite ends of the molding.